Process for converting glow discharge tubes to photoelectric tubes



Aug. 2, 1960 J. P. HAMMER PROCESS FOR CONVERTING GLOW DISCHARGE TUBES TOPHOTOELECTRIC TUBES Filed Feb. 28, 1958 CUTOFF T1 140-150 V. (X

I I!" 9o-1oov V62 INVENTOR JAMES R HAMMER BY WW4??? AGENT United StatesPatent PROCESS FOR CONVERTING GLOW DISCHARGE TUBES TO PHOTOELECTRICTUBES James P. Hammer, Endicott, N.Y., assignor to InternationalBusiness Machines Corporation, New York, N.Y., a corporation of New YorkFiled Feb. 28, 1958, Ser. No. 718,267

"6 Claims. (Cl. 316-9) The invention relates to a process and apparatusfor producing photoelectric devices.

An object of the invention resides in the process whereby a glowdischarge device may be converted into a photoelectric device in a mosteconomical manner.

Another object resides in the use of novel, inexpensive apparatus forcarrying out the process automatically and in a most economical manner.

Other objects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawings,which disclose, by way of examples, the principle of the invention andthe best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 is an electrical wiring diagram of the apparatus for carrying onthe process of the invention.

Fig. 2 is a voltage waveform showing firing and sustaining voltagepoints of the tubes before and after processing.

The glow discharge tube of which there are a variety in commercial use,such as the type NE2, type 6332 and CClL and others, employphoto-emissive electrode structures comprised mainly of coatings ofoxides of such elements as barium and strontium, while others employelectrodes of caesium and other such elements possessing relatively lowwork functions.

In the main the process comprises impressing upon the electrodes of theglow discharge device an alternating current for a period of time thatdepends upon the photoelectric characteristics required. In thisprocess, the photo-emissive material is transferred from the electrodesof the tube and deposited, by what is believed to be a sublimationprocess, upon the inner surface of the envelope surrounding theelectrodes. The envelope is generally made of glass or other materialthrough which light energy, or other forms of "energy capable of thephotoelectric effect, passes to impinge upon the depositedphoto-emissive layer. The period of time mentioned above may be referredto as the aging period.

At this point it might well to consider in the chart below thecharacteristics of one type of glow discharge tube, for example, thetype NEZ. The chart shows the characteristics of ten tube samples beforeand after processing with respect to firing and sustaining volt-agesobtained under dark and light conditions, the firing and sustainingvoltages being identified, respectively, as V and V The processing ofthese ten samples was achieved by applying .to the electrodes, connectedin parallel, a voltagesource of 120 volts rms 60 cycles with a loadresistor of 10,000 ohms connected in series with each tube, and for aperiod of approximately 72 hours. It may be appreciated thatcharacteristics other than those shown in the chart may be realized byvarying the aging period either more or less than the 72 hoursindicated.

2,947,590 Patented Aug. 2, 1960 Before Processing Alter Processing TubeSample Number Dark Light Dark Light Vs V, V V.l Vb V, V V.

It may be appreciated from the first column of figures under Dark V thatthere is a wide tolerance in the dark firing voltages before processingand that the various tubes exhibit very little, if any, photoelectriceffects. After processing, however, it may be noted that the tubes havea marked degree of photoelectric properties as is evidenced by thedifferences in the dark firing volt-ages and the light firing voltages.Moreover, it is to be realized that the aging of these samples forapproximately 72 hours under control of the means described does notresult in consistent characteristics as is evidenced from the fact thatsamples 26 and 36 have dark firing potentials, respectively, of 118volts and 150 volts. It may also be noted that the light firingpotentials for the processed samples range from 104 volts to 128 volts.

The apparatus forming part of the present invention is designed tocontrol the aging process so as to produce converted tubes withcharacteristics that are more nearly consistent. This apparatus is shownin Fig. 2 and comprises three tube stages, respectively, T1, T2 and T3.Stages T1 and T2 are vacuum triodes serving as amplifiers while stage T3is a thyratron having a relay R1 in the plate circuit thereof. The glowdischarge tubes which are to be processed are referenced, respectively,N1, N2, N3 etc. These are shown connected to a circuit path fed by voltsAC. 60 cycle source. This circuit path is further conditioned by apotentiometer K and a relay point Rla associated with the relay R1. Froma point X in this circuit a line is connected to the control grid Tla ofstage T1, a diode D1 at the input thereof serving as a clamp to protectthe grid from an excessive negative voltage. The circuit path containingthe relay Rla contacts, potentiometer K and the lines L1 and L2,connected to the glow discharge tubes, may be called the aging circuit.

The aging operation is carried out in the absence of light. Theapparatus is prepared for operation by first inserting all the tubes tobe aged after which the switch S is closed to apply A.-C. current andvoltage across all the glow discharge tubes connected to the agingcircuit. At the start of the process the potentiometer K will be set soas to provide a relatively high current flow and thereafter, as thetubes age and the current starts to decrease, due to increased voltagedrop across the tubes, the potentiometer is readjusted to provide anearly constant current flow. The current is above the rated current ofthe glow discharge device but below the arc discharge current.

During the initial phase of the operation at least one tube will startto fire, the firing being done during each positive and negative halfcycle. The firing potential will rise with time and as the processcontinues, a second tube will fire. In view of the voltage regulationcharacteristics of these tubes when placed in parallel, the tube thatinitially fired will now fire at random with respect' process iscontinued in this manner until all tubes have fired; 'The aging processcontinues until the firing voltage reaches a predetermined valuewhereupon relay R1 is picked up to open up the Rla relay points in theaging circuit.

By means of this controlled process the converted tubes will havesubstantially similar characteristics within a half of one volt.

In the circuit diagram the tubes T1 and T2 may be either a type 5965 ora type 6211. The tube T3 may be a 2D 2,l.

The potentiometer K has a range of up to 20,000 ohms.

At the start of the aging process tube '11 is in a nonconducting status;consequently, the grid TZa of tube T2 is positively biased to enabletube T2 to conduct heavily, the effect of which is to make the controlgrid T311, of thyrat-ron T3, sufiiciently negative to prevent T3 fromconducting. When, during the course of the aging process, the voltage at'point X exceeds the bias potential on the grid Tia of tube T1,conduction through the latter increases. Consequently, conductionthrough tube T2 drops off and as a result thereof, grid T3a is drivenabove cutoff thereby enabling T3 to fire to energize the relay R1 tostop the aging process. A reset key RK is provided to restore thecircuit to an operating condition for the next process. It may beappreciated that the apparatus may be modified to process tubes of othertypes with diliering'characteristics. This may be done by using circuitcomponents with values appropriate to the process in question and withthe potentiometer K of greater range together with an alternatingcurrent and voltage greater than .120 v. R.M.S.

The AC. waveform in Fig. 2 shows the firing and sustaining voltages ofthe type NEZ tubes. Curve V indicates the dark firing voltage ofunprocessed tubes to be between 65 volts to 75 volts and the sustainingvoltages to be between 45 volts to 55 volts. Curve V shows the darkfiring'voltages of the neon tubes processed according to the invention.These tubes processed according to the invention can be processed withinthe range 1140 volts to 150 volts and can be held to within a half ofone volt tolerance.

While there have been shown and described and pointed out thefundamental novel features of the invention as applied to a preferredembodiment, it will be understood that various omissions andsubstitutions and changes in the form and details of the deviceillustrated and in its operation may be made by those skilled in theart, without departing from the spirit of the invention. It is theintention, therefore, to be limited only as indicated by the scope ofthe following claims. 7 What is claimed is:

1. A process for converting a glow discharge device; of the type havingphoto-emissive material bearing electrodes and having an envelopethrough which energy, capable of the photoelectric effect, istransmitted; to a photoelectric device comprising impressing upon saidelectrodes an alternating current and voltage of sufficient power tocause the depositing of said photo-emissive material to the innersurface of said envelope for a'period of time ranging up toapproximately 72 hours, depending upon the photoelectric characteristicsdesired, and conducting the depositing'of said material i-n'the absenceof light.

2. A process for converting a glow discharge device;

- t 4 of the type having photo-emissive material bearing electrodes andhaving an envelope through which energy, capable of the photoelectriceffect, is transmitted; to a photoelectric device comprising impressingupon said electrodes an alternating current and voltage of sufficientpower above the rated capacity of the glow discharge device to cause thedepositing of said photo-emissive material to the inner surface of saidenvelope for a period of time ranging up to approximately 72 hours,depending upon the photoelectric characteristics desired, and conductingthe depositing of said material in the absence of light.

3. A process for convertinga glow discharge device; of the type havingphoto-emissive material bearing electrodes and having an envelopethrough which energy, capable of the photoelectric efie'c't, istransmitted; to a photoelectric device comprising impressing upon saidelectrodes an alternating current and voltage of sufficient power tocause at a controlled rare thedepositing of said photo-emissive materialto the inner surface of said envelope for a period of time ranging up toapproximately 72. hours, depending upon the photoelectriccharacteristics desired, and conducting the depositing of said materialin the absence or light.

4. A process for converting a glow discharge device; of the type havingphoto-emissive material bearing clectrodes and having an envelopethrough which energy, capable of the photoelectric elf'ect, istransmitted; to a photoelectric device comprising impressing "upon saidelectrodes an alternating current and voltage, the current being abovethe rated current of said glow discharge device but below the arcdischarge current, to cause the depositing of said photo-emissivematerial to the inner surtac'e of said envelope for a period of timeranging up to approximately 72 hours, depending upon the photoelectriccharacteristics desired, and conducting the depositing of said materialin the absence of light.

5. A process for converting a glow discharge device; of the NEZ typehaving photo-emissive material bearing electrodes and having an envelopethrough which light energy, capable of the photoelectric eflfectfistransmitted; to a photoelectric device comprising impressing uponsaidelectrodes an alternating current and voltage, 'ofap'proximately v.R.M.S. value, of suflicient power to cause the depositing of saidphoto-emissive material to the inner surface of said envelope for aperiod of time ranging'up to approximately 72 hours, depending upon thephotoelectric characteristics desired, and conducting the depositing ofsaid material in the absence of light.

6. .A process for converting a glow discharge device; of the NE2 typehaving photo-emissive material bearing electrodes and having an envelopethrough which light energy, capable of the photoelectric effect, istransmitted; to a photoelectric device comprising impressing upon saidelectrodes an alternating current and voltage, of approximately 120 v.R.M.S. value, of sufficient power to cause the depositing of saidphoto-emissive material to the inner surface of said envelope fora'period of time or approximately 72 hours and conducting the depositingof said material in the absence of light.

References Cited in the file of this patent UNITED STATES PATENTS1,955,794 Du Mont et al .t Apr. 24, 1934 2,701,849 Penning et a1. Feb.8, 1955 2,804,365 Flowers Aug. 27, 1957 2,809,087 Veith Oct. 8, 1 57FOREIGN PATENTS 601,870 Great Britain May 13,1948

